The production of molded articles from homogeneous materials, foams, structural foams, or integral skin foams, based, in particular, on polyurethane has become commercially very important. In particular, more and more molded articles are produced from the above-mentioned materials which must have high strength and, in some cases, will have surfaces which, when in use, are visible. The discharge of such liquid reaction mixtures from the mixing chamber and the subsequent introduction into the mold is particularly critical for the quality of the molded articles. In particular, highly viscous reaction mixtures are very difficult to prepare. The problem is further aggravated by the fact that more and more solid additives in the form of powder or small-particles or fillers have to be introduced into the cavity of the mold with the reaction mixture. These additives or fillers generally increase the viscosity. Many attempts have therefore been made to prevent any of the reactants from entering the cavity unmixed; to prevent air from entering the reaction mixture on the way from the mixing chamber to the cavity and in the cavity itself; to prevent turbulence which could cause streaks; and to prevent an uneven flow front of reaction mixture from building up. It is generally known that these problems can be overcome by means of a flow of reaction mixture which is as laminar as possible.
Various solutions have been found and are adequate in individual cases. The simplest solution is to allow the reaction mixture to flow into the open mold sufficiently slowly for it to flow into a laminar stream to the deepest part of the mold over a plane which is inclined as slightly as possible. Turbulence and cascading flows must be avoided. However, clearly, such a method of manufacture is not economical. This method is also not suitable for charging materials into closed molds since the filling procedure is not observable. Other solutions make use of a specially shaped runner. However, with these solutions it is necessary to provide specific operating conditions, for example with respect to the flow rate and viscosity of the reaction mixture, so that the apparatus cannot be used with all reacting systems. It has therefore already been proposed that the runner should be arranged in an exchangeable component so that the same apparatus may be operated with different runners and under different conditions. This necessarily means a greater expense.
Finally, an apparatus has been described in which an adjustable baffle plate is arranged opposite the outlet opening of the mixing chamber. The distance between the baffle plate and the outlet opening is adjustable to enable a perfect expanding flow to be obtained. However, the distance is fixed during the filling process. It is, of course, possible to move the baffle plate back just before the filling process ends so that it forms a plane surface with the wall of the mold in which it is placed. The entire space between outlet opening and baffle plate is thus completely filled upon completion of the filling process since, in this previously known apparatus, the space between the outlet opening of the mixing chamber and the baffle plate also forms part of the cavity of the mold so that the finished molded article also has a suitable thickness in this section (see e.g., German Pat. No. 2,348,658 and U.S. Pat. No. 3,991,147).
The object of the invention is therefore to find a method and an apparatus which ensures the production of molded articles which are substantially free of defects even under varying operating conditions, as is often required when changing the throughput or the viscosity of the reaction mixture.